The metabolism of inorganic pyrophosphate (PPi) is being studied in organ cultures of hyaline- and fibro-cartilages from rabbits and dogs. All cartilages produce PPi, but immature cartilage produces more than adult cartilage and hyaline cartilage produces more than fibrocartilage. Inhibitors of glycosamino-glycan synthesis are being used to determine if the source of the secreted PPi can be identified. Skin fibroblasts from normal subjects and from patients with a hereditary form of calcium pyrophosphate dihydrate crystal deposition disease are being grown in monolayer culture. Intracellular PPi levels will be determined in each as part of the search for a biochemical marker in this condition. The capacity of crystals of various chemical composition or of various crystal lattice with the same chemical composition to lyse erythrocyte membranes is being tested and compared with the capacity of these crystal surfaces to adsorb proteins such as IgG and albumin. The fate of IgG adsorbed to sodium urate crystals after phagocytosis has occurred is being explored.